Primary Rosai-Dorfman disease of bone without lymphadenopathy diagnosed by fine needle aspiration cytology. A case report.

Background: Solitary bone involvement without lymphadenopathy is a rare manifestation of Rosai-Dorfman disease, or sinus histiocytosis with massive lymphadenopathy (SHML). Only 11 cases have been reported in the literature to date, all diagnosed on histology.

Methods: A 7-year-old girl had a radiolucent, lytic lesion in the shaft of the tibia clinically simulating Ewing's sarcoma. Fine needle aspiration cytology (FNAC) showed a microscopic picture typical--of SHML. There was no lymphadenopathy.

Conclusions: Rosai-Dorfman disease sometimes involves bone without lymphadenopathy and can be diagnosed confidently on FNAC. To the best of our knowledge, this is the 12th case report of solitary bone involvement.